genetics of living systems

Question 1

What is a mutation and how could it occur?

Answer 1

Change in the sequence of bases in the DNA which can disrupt protein synthesis

Through substitution, deletion or insertion of one or more nucleotides

Question 2

What is a frame shift?

Answer 2

A mutation which occurs during an insertion or deletion of a nucleotide.

Addition or deletion which change the reading frame of amino acids and change every excessive read codon from the point of the mutation

Question 3

What type of substitution mutations can occur?

Answer 3

Silent: A substitution that does not alter the amino acid sequence of polypeptide due to the degenerate nature of the genetic code
Missense: Alters a single amino acid in the polypeptide chain
Nonsense: Creates a premature stop codon which stops the translation of mRNA leading to the production of an incomplete polypeptide

Question 4

What are the two effects of mutations?

Answer 4

Can have damaging mutations that may stop the synthesis of useful proteins or useful mutations that provide a useful characteristic

Question 5

What is a chromosome mutation?

Answer 5

A chromosome mutation is a mutation which affects the whole chromosome rather than a section of DNA which can be caused by mutagens.

Question 6

What are the types of ways chromosome mutations can occur?

Answer 6

1) Deletion: A section of a chromosome breaks off and is lost
2) Duplication: A section gets duplicated on the chromosome
3) Translocation: A section of the chromosome will break off and join another non-homologous chromosome
4) Inversion: Section will break off, reverse and rejoin

Question 7

What are mutagens?

Answer 7

Mutagens are biological, chemical or physical agents which can alter the rate at which mutations can occur

Question 8

Why is gene regulation required?

Answer 8

Because certain proteins such as hormones are only required by certain cells at certain times to carry out a short lived response.

The entire genome of an organism is present in the nucleus, including genes not required by the cells therefore expression must be controlled by turning on and off certain genes.

This prevents vital resources being wasted,

Question 9

In what ways are the genes regulated?

Answer 9

Transcriptional: Genes can be turned on or off
Post Transcriptional: mRNA can be modified to regulate translation
Translational: Translation can be stopped or started
Post translational: Modification of proteins after synthesis

Question 10

What are histones?

Answer 10

DNA are wound around proteins called histones allowing them to be packed into the nucleus

Question 11

What is the difference between heterochromatin and Euchromatin?

Answer 11

Heterochromatin is when DNA is tightly wound around histones whereas Euchromatin is loosely wound around the histones.

Question 12

Why can genes not be transcribed when tightly wound around the histone? (Heterochromatin)

Answer 12

RNA polymerase cannot accsess the genes for translation whereas in losely wound DNA can be freely transcribed.

Question 13

How can chromatin remodelling be used to prevent energy consumption?

Answer 13

Makes it so that during any other phases of cell division besides from interphase, DNA will be wound tightly as heterochromatin to prevent energy consumption as high energy is required in DNA replication.

Question 14

How can the strength of DNA wounding around a histone be altered?

HINT: chemistry groups

Answer 14

Histones are (+) whereas DNA is (-)

Acetylation will reduce the positive charge on the histones and make DNA coil less tightly
Methylation will make histones more hydrophobic so they bind more tightly and prevent the transcription of genes.

Question 15

What is an operon?

Answer 15

An Operon is a group of genes that are under the control of the same regulatory mechanism which are expressed at the same time.

Question 16

What is the lac operon and what is it responsible for?

Answer 16

The lac operon consist of three genes involved in the metabolism of lactose an can be transcribed into a single long mRNA molecule.

Question 17

How are the enzymes required for lactose metabolism coded for using the lac operon?

Answer 17

When lactose is present, it binds to the repressor protein and causes it to change shape and no longer bind to the operator.
RNA polmyermase can bind to the promotor and the genes are transcribed and enzymes are synthesised

Question 18

What is a repressor in an operon?

Answer 18

A repressor is consistently produced and binds to the operator to prevent RNA polymerase binding to DNA and starting transcription. This is coded for via a regulatory gene.

Question 19

What does the cyclic AMP do?

Answer 19

By binding cAMP receptor protein with cAMP, this will increase the rate at which transcription occurs when RNA polymerase binds to the promotor which is required to produce the quantity of enzymes needed to metabolise lactose

Question 20

How can a pre-RNA molecule be modified before binding to a ribosome?

Answer 20

mRNA can be stabilised by adding a cap which is a modified nucleotide to the 5’ end and a tail which is a long chain of adenine molecules to the 3’ end which delays degradation in the cytoplasm and assists in mRNAs binding to the ribosome.

Question 21

What is the difference between introns and extrons?

Answer 21

Introns: non-coding DNA
Extrons: coding DNA

Question 22

What is splicing?

Answer 22

When RNA is cut at a specific point so the introns are removed and the exons are joined together.

Question 23

How else can RNA be edited other than splicing and placing a cap and tail?

Answer 23

mRNA molecule sequences can be changed by addition, deletion and substitution which can result in the same effect as a point mutation which increases the range of proteins produced.

Question 24

What are some examples of translational control?

Answer 24

+The more resistant mRNA is made, the longer it will last in the cytoplasm and the greater quantity of protein will be synthesised
+Binding of inhibitory proteins to mRNA can prevent it from binding to ribosomes to stop protein synthesis
+Activation of initiation factors can help mRNA bind to ribosomes

Question 25

What are protein kinases?

Answer 25

Enzymes that catalyse the attachment of phosphate groups to proteins which can alter tertiary structures and protein structure

Question 26

How can proteins be modified after translation/ being synthesised? (Post translational control)

Answer 26

+ Addition of non-protein groups
+ Modifying amino acids/the formation of bonds
+ Folding of shortening proteins
+ cAMP modification

Question 27

What are transcription factors?

Answer 27

Proteins that bind to specific DNA sequences and control the rate at which DNA is transcribed to RNA

Question 28

What are homeobox genes?

Answer 28

A gene with DNA sequences that code for a protein transcription factor which attach to DNA that regulate transcription by turning genes on and off in an order.

Question 29

What are Hox genes?

Answer 29

A subset of homeobox genes that are only found in animals and determine embryonic regions.

The direct linear order of hox genes will order how the regions of the body are developed.

Question 30

What is the difference between necrosis and apoptosis?

Answer 30

Necrosis: Uncontrollable cell death after trauma
Apoptosis: Controlled cell death

Question 31

How does apoptosis occur?

Answer 31

1) The cell will shrink
2) DNA and protein is broken down
3) Mitocondria will degrade
4) Blebs develop and are engulfed by phagocytes

Question 32

Why may cells go under apoptosis?

Answer 32

Defence against pathogens or dangerous/damaged cells or a part of a normal developmental process